In the present study, alkaline hydrothermally treated titania nanoparticles (TiO2-HT) are prepared and followed by calcination at different low temperatures to improve TiO2 activity under visible light. The prepared photocatalysts (PCs) are characterized by different tools. TiO2-HT is scrutinized for decontamination of para-nitrophenol (PNP) and hexavalent chromium ions (Cr6+ ions) under simulated sunlight. TiO2-HT-300 and TiO2-HT-400 PCs have nanosized particle with large surface area of 148 and 116.26 m2/g, respectively. Additionally, XRD and FTIR proved formation of nanocrystalline anatase TiO2. The different calcined TiO2-HT materials show lower adsorption capacity for PNP and Cr6+ ions. TiO2-HT-300 and HT-TiO2-400 PCs have higher reduction rate of PNP than that of uncalcined temperature titania (HT-TiO2-U) powder. Complete conversion of PNP is achieved at natural pH after 180 min over TiO2-HT-300. As well, TiO2-HT-300 exhibits a superior photocatalytic removal of Cr6+ ions. The enhanced photocatalytic efficacy is ascribed to the synergism between higher surface area and particle size (quantum effect) of TiO2-HT-300. As results, HO· radicals are the main key active species for the photocatalytic degradation of PNP over TiO2- HT-300 PC but contribution of O2– and h+ holes is minor. The used method for preparation of TiO2-HT-300 reduces the cost preparation as well as environmental impact reduction. Finally, low temperature-calcined TiO2 is promising visible light active and an efficient photocatalyst with lower environmental impact for detoxification of PNP and Cr6+ ions from water.

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Photoreduction of chromium hexavalent ions (Cr6+) from the aquatic environment is urgently needed due to its impairing effect on human health. Adsorption, photoreduction, and desorption of reduced trivalent chromium (Cr3+) at the photocatalyst surface are all significant factors for determining photocatalytic reduction efficiency. Herein, we report a facile, template-free hydrothermal approach to fabricate green and homogeneous mixed-phase (1 T/2H) molybdenum disulfide (MoS2) nanosheets for highly efficient removal of Cr6+ ions and pharmaceuticals from wastewater. The nanostructure and morphology of the obtained (1 T/2H) MoS2 are investigated; the calculated crystallite size of the (2H/1 T) MoS2 nanosheets is found to be 1.7 nm. The presence of surface functional groups adsorption, and photoreduction processes is confirmed by spectroscopic studies using Fourier transform infrared (FTIR) spectra. Additionally, Raman spectra confirmed the formation of 1 T/2H mixed-phase MoS2 which illustrates its crystal phases, structure, and chemical composition. Moreover, the point-of-zero charge analysis revealed the positively charged surface in the acid system. The obtained results revealed the non-toxicity of MoS2 nanosheets at doses lower than 1000 ppm. The results reveal that the (1 T/2H) MoS2 exhibited impressive reduction performance for Cr6+; the reduction efficiency of chromium Cr6+ is 100% under simulated sunlight, 90 min at pH (3). Further spectroscopic study results confirm the importance of the adsorption step in Cr6+ ions photoreduction. Different pharmaceuticals are also completely degraded over (1 T/2H) MoS2 nanosheets. Interestingly, complete removals of E. coli O157:H7, Listeria monocytogenes, and Candida albicans were observed at a dose of MoS2 nanosheets of 250 ppm after a contact time of 30, 30, and 45 min, respectively. The results of the current work could lead to a rational design of high-performance nanosheets for the efficient decontamination of heavy metals, pharmaceuticals, and pathogens from aquatic environments. Graphical abstract

The present work investigated the utilization of dead biomass of the highly multi-heavy metals tolerant indigenous fungal strain NRCA8 isolated from the mycobiome of fertilizer industry effluents that containing multiple heavy metal ions at high levels to remove Pb2+, Ni2+, Zn2+, and Mn2+ as multiple solutes from multi-metals aqueous solutions for the first time. Based on morphotype, lipotype and genotype characteristics, NRCA8 was identified as Cladosporium sp. NRCA8. The optimal conditions for the bioremoval procedure in the batch system were pH 5.5 for maximum removal (91.30%, 43.25%, and 41.50%) of Pb2+, Zn2+ and Mn2+ but pH 6.0 supported the maximum bioremoval and uptake of Ni2+ (51.60% and 2.42 mg/g) by NRCA8 dead biomass from the multi-metals aqueous solution, respectively. The 30 min run time supported the highest removal efficiency and uptake capacity of all heavy metals under study. Moreover, the equilibrium between the sorbent NRCA8 fungal biomass and sorbates Ni2+, Pb2+ and Zn2+ was attained after increasing the dead biomass dose to 5.0 g/L. Dead NRCA8 biomass was described by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectrometer before and after biosorption of Pb2+, Ni2+, Zn2+ and Mn2+ under multiple metals system. The Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms were applied to characterize the adsorption equilibrium between Pb2+, Ni2+, Mn2+ and Zn2+ and the adsorbent NRCA8. By comparing the obtained coefficient of regression (R2) by Freundlich (0.997, 0.723, 0.999, and 0.917), Langmiur (0.974, 0.999, 0.974, and 0.911) and Dubinin-Radushkevich (0.9995, 0.756, 0.9996 and 0.900) isotherms values for Pb2+, Zn2+, Ni2+ and Mn2+ adsorption, respectively, it was found that the isotherms are proper in their own merits in characterization the possible of NRCA8 for removal of Pb2+, Zn2+, Ni2+ and Mn2+. DKR isotherm is the best for Pb2+ and Ni2+ (0.9995 and 0.9996) while Langmiur isotherm giving a good fit to the Zn2+ sorption (0.9990) as well as Freundlich isotherm giving a good fit to the Mn2+ sorption (0.9170). The efficiencies of Cladosporium sp. NRCA8 dead biomass for bioremoval of heavy metals from real wastewater under the optimized conditions were Pb2+, Ag+, Mn2+, Zn2+ and Al3+ ˃ Ni2+ ˃ Cr6+ ˃ Co2+ ˃ Fe3+ ˃ Cu2+ ˃ Cd2+. Dead NRCA8 biomass showed efficient ability to adsorb and reduce harmful components in the industrial effluents to a level acceptable for discharge into the environment.